The Program Project for Marrow Transplantation in Leukemia is an integrated multidisciplinary program of basic and clinical research aimed at elucidating the genetic, cellular and environmental factors which includes the development of transplanted hematopoietic and lymphoid progenitor cells with an allogeneic host. This project is principally focused on the distinctive biology of T-cell depleted marrow transplants applied to the treatment of leukemia. The primary emphasis is given to the development of a clearer understanding of the biological forces promoting or limiting engraftment, the development of innovative strategies to prevent graft failure or rejection, and their evaluation in both murine and primate models of transplantation. Research programs are also proposed to investigate cellular systems contributing to resistance to leukemia recurrence and the development of graft/host tolerance. In addition, experimental programs exploring the pathogenesis of CMV infections and new approaches to diagnosis, treatment and prevention of these infections based on recently developed human monoclonal antibodies are proposed. As an extension of this research program, clinical trials are proposed to evaluate both HLA matched and non-identical related as well as matched unrelated T-Cell depleted marrow transplants in the treatment of leukemia and to assess new cytoreductive and immunosuppressive approaches designed to abrogate resistance to engraftment and to further reduce the incidence of leukemia in the post transplant period.